The present invention relates to a photosensitive resin composition (resist composition) that are suitable for forming minute patterns such as semiconductor integrated circuits using, for example, ultraviolet rays or far-ultraviolet rays (including excimer laser), and a process for forming a pattern using the same.
With rises in the integration level and performance of semiconductor integrated circuits, there has been demand for resists with better resolution (patterns in submicron order, quartermicron order, or smaller) and for improvements of processing latitude. To meet such demand, improvement of resolution, as well as resists themselves, by employing a conventional lithography technique has been proposed. For example, in the case where the wavelength of light is in the neighborhood of the resolution limit, there is proposed a multi-layer process in which, utilizing the fact that a silicon-containing resist is highly resistant to oxygen plasma, the resolution is improved by oxygen plasma. According to this process, in the case where a double-layered resist is to be formed, on a lower resist layer formed on a substrate is applied a silicon-containing resist such as a vinyl group-containing polysiloxane, the resist is patterned, and then the lower layer (undercoat layer) is etched by oxygen plasma etching.
This process, however, has the drawbacks that synthesis of polysiloxane-based resists rendered photosensitive becomes complicated and thus results in a rise in cost and that it is difficult to control, with good repeatability, the content of silicon giving a large influence on oxygen plasma resistance. The silicon content and the performance of a resist (sensitivity, resolution) are generally in a conflicting relation. That is, increasing the silicon content improves oxygen plasma resistance but deteriorates the performance of a resist. Decreasing the silicon content improves the performance (sensitivity, resolution) of a resin but leads to degradation of oxygen plasma resistance. For such reasons, improving the performance (sensitivity, resolution) of a resist while maintaining the oxygen plasma resistance is difficult.
On the other hand, there have been known compositions comprising an alkali-soluble novolak resin and a diazonaphthoquinone derivative as single resists for semiconductors. Utilizing the characteristic that a diazonaphthoquinone group is decomposed upon irradiation with light of 300 to 500 nm wavelength to form a carboxyl group, allowing the compositions to change from an alkali-insoluble state to an alkali-soluble state, these photosensitive resin compositions have been used as positive resists.
In such semiconductor resists, the most conventional method for achieving miniaturization or minuter integrated circuits is to use an exposure light of a shorter wavelength.
For example, instead of using g-ray (wavelength: 436 nm) or i-ray (Wavelength: 365 nm) of high-pressure mercury lamps generally used, a light source of a shorter wavelength such as KrF excimer laser (wavelength: 248 nm) and ArF excimer laser (wavelength: 193 nm) of next generation have already come into practical use.
However, the use of novolak resin/diazonaphthoquinone-type positive resists having been employed in the production of semiconductor integrated circuits with g-ray or i-ray leads to considerable deterioration in sensitivity and resolution even with KrF excimer laser or ArF excimer laser because of the absorption by the novolak resin. Therefore, the novolak resin/diazonaphthoquinone-type positive resists are lacking in practicability.
Moreover, minute processing with KrF or ArF excimer laser has a number of technical problems to be solved with respect to the choice of, for example, exposing devices such as light sources a lens system, and photosensitive materials (resists). In addition, plant investment for applying the minute processing with KrF or ArF excimer laser to the practical production of semiconductors will be a vast sum of money.
Recently, resists, which are etched, of high-melting point metal substrates (e.g., aluminum-copper, silicides) for use in the fabrication of semiconductors have been required to have higher heat resistance and dry etching resistance than that of conventional novolak resin-series resists. Since resists for KrF or ArF excimer laser processing irreplaceable by novolak resin-based resists are, from a material restriction viewpoint, generally poorer in heat resistance and dry etching resistance than novolak-series resists, improvement of such characteristics has been desired.
Accordingly, it is an object of the present invention to provide, utilizing a conventional resist or lithography technique, a photosensitive resin composition with improved oxygen plasma resistance, heat resistance, and dry etching resistance; a process for producing the same; and a process for forming a pattern.
It is another object of the present invention to provide, even in the case of resists currently in use, a photosensitive resin composition as a resist with largely improved sensitivity and resolution and useful in forming a minute pattern; a process for producing the same; and a process for forming a pattern.
It is still another object of the present invention to provide a photosensitive resin composition capable of largely improving the profile of a pattern and focus latitude; a process for producing the same; and a process for producing the same.
The inventors of the present invention made intensive and extensive studies to achieve the above-mentioned objects and finally found that the addition of an inorganic substance in the form of uneven particles to a resist made from an alkali-soluble resin or the like largely improves not only its oxygen plasma resistance but also heat resistance and dry etching resistance, and that the use of inorganic particles having a mean particle size transparent to the wavelength of exposure light improves the sensitivity and resolution of a resist. The present invention was accomplished based on the above findings.
That is, the photosensitive resin composition of the present invention comprises a photosensitive resin and inorganic particles having a functional group and is substantially free from a hydrolytic polymerizable organic metal compound or its condensate. The mean particle size of the inorganic particles is usually smaller than the wavelength of light to which the resuting resist is to be exposed, for example about 1 to 100 nm. The inorganic particles can be of colloidal silica. The photosensitive resin composition may be of negative or positive type and is preferably developable with water or an alkali. The amount of the inorganic particles is, on a solid matter content, about 10 to 500 parts by weight relative to 100 parts by weight of the photosensitive resin.
The process of the present invention includes a process for forming a pattern without baking, comprising applying the above-mentioned photosensitive resin composition onto a substrate followed by exposure to light and development. A pattern may be formed through a process comprised of, using the photosensitive resin composition described above as the upper layer in a double-layered resist, exposure to light, development not followed by baking, oxygen plasma treatment using the pattern of the upper layer as a mask, and the transfer of the upper pattern to the lower.